A liquid crystal display device acting as a video display device illuminates a liquid crystal panel with an LED backlight including an array of light-emitting diodes (LEDs).
For such a video display device, a technique called “local contrast control” is particularly known (e.g., Japanese Patent Laid-Open No. 2001-142409). In this technique, LEDs are two-dimensionally arranged directly under a liquid crystal panel and the brightness of the LED is controlled according to the feature quantity of a video signal, mainly an intensity value. Such local contrast control can improve the contrast of a displayed image.
In recent years, video display devices with a 3D (three-dimensional) display function (hereinafter, will be called 3D-TVs) have been announced one after another. A 3D-TV displays a left-eye image and a right-eye image at the same time or in a time sharing manner, allowing a viewer to recognize a three-dimensional image. The former method will be called an image segmentation system while the latter method will be called a time-sharing system.
In the future, local contrast control is expected to be introduced to 3D-TVs. A feature quantity in the local contrast control needs to be detected for each of a left-eye image and a right-eye image. The intensity of an LED backlight needs to be alternately switched between a left eye and a right eye based on the set intensity value of the LED backlight, particularly in the time-sharing system. The set intensity value is determined according to the feature quantity.
FIG. 14 illustrates a typical configuration of a 3D-TV of the time-sharing system having a local contract control function. FIG. 14 is a block diagram illustrating a liquid crystal display device 1000 that displays full high definition (FHD) images for left and right eyes in a time sharing manner with a frequency of 120 Hz. Shutter glasses in synchronization with the switching of left and right displayed images are worn to enable stereoscopic vision.
As shown in FIG. 14, the video display device 1000 receives FHD video signals of two systems: a right-eye video signal 1001a and a left-eye video signal 1001b. A video signal transmitted in a 3D transmission format of High-Definition Multimedia Interface (HDMI) is outputted after undergoing expansion, I/P (Interlace/Progressive) conversion, and so on in a circuit (not shown) preceding the configuration of FIG. 14. FIG. 15A shows the state of the output. As shown in FIG. 15A, the right-eye video signal 1001a and the left-eye video signal 1001b are in phase (simultaneously inputted) with a frame period of 60 Hz. A liquid crystal drive unit 1002 displays an image on a liquid crystal panel 1003 based on the video signals 1001 (1001a, 1001b). The liquid crystal panel 1003 is illuminated with light from the back by an LED backlight 1005 driven by an LED driver 1004. In this configuration, the video display device 1000 includes two local control units 1006 (right-eye local control unit 1006a and left-eye local control unit 1006b) that determine the light quantity of an LED for illuminating an image according to a feature quantity for each of right and left eyes, and a selector (selecting unit) 1007 that transmits results determined by the local control units 1006, to the LED driver 1004 while switching the results every 120 Hz. As shown in FIG. 15B, a displayed image and an inputted image are provided at different times, and thus the video display device 1000 further includes a delay adjusting memory 1008 that absorbs the difference. Hence, when the liquid crystal panel 1003 displays a right-eye image, the LED backlight 1005 is illuminated according to the feature quantity of the right-eye video signal 1001a in the previous frame. When a left-eye image is displayed, the LED backlight 1005 is illuminated according to the feature quantity of the left-eye video signal 1001b in the previous frame.
In the video display device 1000 of the conventional configuration, however, communications relating to LED light emission intensity are carried out with the LED driver 1004 every 120 Hz. Thus, unfortunately, large extraneous radiation may occur at this point and other electronic components may be adversely affected by noise.
The present invention has been devised in consideration of this point. An object of the present invention is to provide a video display device that can achieve local control for high-quality 3D images while reducing extraneous radiation.